1. Field of the Invention
Apparatus for measuring the axial length of the human eye or another layered object, and more particularly, interferometric apparatus for measuring the axial length of the human eye with high precision and high speed.
2. Description of Related Art
The United States population of people over 65 years old is expected to exceed 70 million in 2030. World populations of the elderly are increasing at a similar rate. Accordingly, there is a significant and growing need for tools to treat the high incidence of eye diseases and related problems that are expected within that demographic. Cases of diabetic retinopathy, glaucoma, macular degeneration, and cataract disease will likely climb tremendously in the next few decades. Information about the structure of the eye is required in surgeries for these diseases, and in surgeries that deal with replacement of the crystalline lens of the eye. Choosing a correct intraocular lens (IOL) is a crucial step in this procedure.
The choice of an optically correct intraocular lens requires detailed knowledge of the precise geometry of the particular eye. This in turn requires an apparatus and method for precise and accurate measurement of eye geometry. One technique that can be used to measure a layered structure is long-range time-domain low-coherence interferometry (TD-LCI). TD-LCI is used in many fields such as microscopy, sensing applications, and quality control in semiconductor manufacturing and other industries.
The eye is a layered structure. However, heretofore the use of TD-LCI in the measurement of the distances between optical interfaces inside a human eye has been limited due to its slow measurement speed, low range and low sensitivity. In attempting to measure the geometry of an eye using TD-LCI, measurement speed defines the accuracy of the method since the measurements are performed on a live patient's eye, which is subject to a small jitter. Additionally, high measurement sensitivity is required to detect weak scattering from the tissue-liquid interfaces within the eye.
Currently, a majority of the ophthalmologists use less precise ultrasound and other instruments for eye measurement, but are interested in obtaining improved eye measurement tools. There are over 20,000 hospitals, ambulatory surgical centers, and offices used by the more than 16,000 ophthalmologists and 32,000 optometrists within the United States that could use such improved tools, and many more locations worldwide.
What is needed, therefore, is a measurement apparatus that has a sufficiently high measurement speed so as to perform a complete measurement of the geometry of an eye faster than the occurrence of eye jitter, while also having sufficient sensitivity to detect the tissue-liquid eye interfaces, and sufficient range so as to be able to measure all of the interfaces of the eye, from the outer corneal surface to the retinal surface.